Flexible shafts comprise basic elements of power transmission and are designed to transmit power or control from a driving element to an element to be driven. Transmission may be over, under, or around obstacles or objects where transmission by solid shafts would be impractical or impossible.
In a typical or conventional rotatable flexible shaft, a wire mandrel has a plurality of layers of closely coiled wire wound thereover, each of the layers being successively wound over another in alternately opposing directions, i.e., right or left-hand lay. This shaft is usually covered by a flexible casing, matallic or covered, and a clearance between the shaft and casing is provided in order that the shaft may rotate freely within the casing.
Rotatable flexible shafts are of two basic types--power driven and remotely controlled. Power driven flexible shafts are designed primarily for motor-driven or high speed operation in one direction. Remote control flexible shafts, on the other hand, are designed primarily for hand-operated control, usually 100 rpm or less, or intermittent high speed use, in either direction of rotation.
The present flexible shaft device may be used advantageously in either power driven or remote control applications.
Typical power driven applications of the present flexible shaft assembly include fan drives in confined spaces, as aboard submarines, for example; operating of portable power tools in cramped areas; and the like.
In most remote control applications, a minimum amount of torsional deflection, or "lag", between the control and controlled element is permissible, regardless of the direction of rotation of the shaft. It is virtually impossible to entirely eliminate torsional deflection, unless solid shafts are employed, because of the alternate layers of wires either winding or unwinding when the shaft is subjected to the torsional load. Regardless of the direction of rotation of the flexible shaft, it should operate smoothly and be free of any tendency to "jump".
A typical remote control application of the present composite assembly involves its use in automobile steering mechanisms. Flexible shafts improve the ability of the steering column to absorb energy in a frontal impact situation. The flexible shaft has one of its ends operably connected to the bottom of the steering shaft while its other end may be connected to some suitable coupling means capable of absorbing considerable road induced shake. At least one domestic car manufacturer requires the presence of a short flexible shaft in its steering mechanism to maintain a sinuous curve while rotating in either direction and yet be capable of transmitting high torques.
The present invention provides a balanced composite flexible shaft assembly capable of transmitting high torques while operating in a tight radius. The assembly comprises a central shaft which is permanently affixed at each end thereof to an end fitting member, and a plurality of shafts spaced outwardly of the central shaft and disposed symmetrically therearound, which outer shafts are permitted to free float in at least one of the end fittings. The entire assembly may be substantially torsionally balanced by employing right and left lay shafts. The central shaft and outer shafts are conventional rotatable flexible shafts.
Unbalanced torsional deflection of rotating flexible shafts is due primarily to the alternate lay of each successive layer of wires, i.e., a torsional load applied to the shaft in a "wind" direction which tends to tighten up the outer layer of wires will exhibit a lower deflection value than when subjected to an identical load in the unwind direction, which tends to loosen the wires of the outer layer.
Torsional deflection of flexible shafts is readily calculable. By selecting the direction of lay of the central and each of the outer shafts, and sizes, if necessary, substantially balanced torsional deflection of the present assembly may be achieved.